std.stdio.File.readln
- multiple declarations
Function File.readln
Read line from the file handle and return it as a specified type.
S readln(S)
(
dchar terminator = '\x0a'
)
if (isSomeString!S);
This version manages its own read buffer, which means one memory allocation per call. If you are not
retaining a reference to the read data, consider the File
version, which may offer
better performance as it can reuse its read buffer.
Parameters
Name | Description |
---|---|
S | Template parameter; the type of the allocated buffer, and the type returned. Defaults to string . |
terminator | Line terminator (by default, '\n' ). |
Note
String terminators are not supported due to ambiguity with readln(buf) below.
Returns
The line that was read, including the line terminator character.
Throws
StdioException
on I/O error, or UnicodeException
on Unicode conversion error.
Example
// Reads `stdin` and writes it to `stdout`.
import std .stdio;
void main()
{
string line;
while ((line = stdin .readln()) !is null)
write(line);
}
Function File.readln
Read line from the file handle and write it to buf[]
, including
terminating character.
size_t readln(C)
(
ref C[] buf,
dchar terminator = '\x0a'
)
if (isSomeChar!C && is(Unqual!C == C) && !is(C == enum));
size_t readln(C, R)
(
ref C[] buf,
R terminator
)
if (isSomeChar!C && is(Unqual!C == C) && !is(C == enum) && isBidirectionalRange!R && is(typeof(terminator .front == (dchar) .init)));
This can be faster than line = File
because you can reuse
the buffer for each call. Note that reusing the buffer means that you
must copy the previous contents if you wish to retain them.
Parameters
Name | Description |
---|---|
buf | Buffer used to store the resulting line data. buf is enlarged if necessary, then set to the slice exactly containing the line. |
terminator | Line terminator (by default, '\n' ). Use
newline for portability (unless the file was opened in
text mode). |
Returns
0 for end of file, otherwise number of characters read.
The return value will always be equal to buf
.
Throws
StdioException
on I/O error, or UnicodeException
on Unicode
conversion error.
Example
// Read lines from `stdin` into a string
// Ignore lines starting with '#'
// Write the string to `stdout`
import std .stdio;
void main()
{
string output;
char[] buf;
while (stdin .readln(buf))
{
if (buf[0] == '#')
continue;
output ~= buf;
}
write(output);
}
This method can be more efficient than the one in the previous example
because stdin
reuses (if possible) memory allocated
for buf
, whereas line = stdin
makes a new memory allocation
for every line.
For even better performance you can help readln
by passing in a
large buffer to avoid memory reallocations. This can be done by reusing the
largest buffer returned by readln
:
Example
// Read lines from `stdin` and count words
import std .array, std .stdio;
void main()
{
char[] buf;
size_t words = 0;
while (!stdin .eof)
{
char[] line = buf;
stdin .readln(line);
if (line .length > buf .length)
buf = line;
words += line .split .length;
}
writeln(words);
}
This is actually what byLine
does internally, so its usage
is recommended if you want to process a complete file.
Authors
Walter Bright, Andrei Alexandrescu, Alex Rønne Petersen